CompositesWorld
Issue link: https://cw.epubxp.com/i/546021
AUGUST 2015 46 CompositesWorld FEATURE / STRUCTURAL HEALTH service. Tey require periodic visual inspection supported by NDT (e.g., ultrasonics, eddy current). Inspection intervals are based on fxed in-service time or cycles and are prescribed for all aircraft of a given model. Very often, no damage is found, yet a huge amount of time must nevertheless be consumed dismantling and reas- sembling the aircraft to access and inspect these structures. Airbus has several programs in place to explore SHM implementation in composite structures with a view toward enabling condition-based maintenance (CBM) — triggering inspections based on actual health indications of each aircraft's structures instead of feet- wide fxed time periods. Tis is also one of the goals of the FAA's programs via the AANC at Sandia. One illustration is the acousto-ultrasonics (AU) system Airbus is developing to detect stringer disbond in composite structures surrounding the doors on its A350 XWB. Data show this region accounts for the majority of in-service fuselage damage on long- haul aircraft, with 15% of impacts sustained by doors, 22% amassed in cargo door surrounds and 31% accumulated in passenger door surrounds. Current CFRP fuselage areas have been designed and tested to sustain such impact damage, but any visible damage still must be inspected using NDT. Using SHM sensors would alle- viate concern about impacts that don't produce visible damage, as well as do away with the need to inspect from inside the aircraft structure, which can involve time-consuming removal of interior sidewalls and other systems, resulting in lost fight revenue, espe- cially when unscheduled. "Airlines estimate that $150,000 to $200,000 in revenue is lost for every day a narrowbody aircraft is not in service," says Chandler, "and $500,000 per day is lost for widebody aircraft." Te AU system now in testing uses a specially designed network of Acellent Technologies' SMART Layer sensors — polyimide flms in which piezoelectric sensors are strategically distributed to communicate with each other by sending and receiving ultrasonic surface waves (Lamb waves). Tese provide damage assessment based on software analysis of the signal disruptions and changes in patterns vs. baseline data. Sensors are easily installed using aerospace-grade adhesives. When a handheld SCAN Genie diag- nostic unit is plugged into SMART Layer sockets, it can indicate the damage location and size or simply display a red/green signal to indicate damage/no damage in the structure. Te system also can be designed to connect to onboard diagnostic units for on-demand or automated interrogation. Airbus has two fight validators: an A350 and the MSN001 A340 fight-test aircraft retroftted with an A350 XWB CFRP skin panel in the surround structure of passenger door 1 (see Fig. 2, above). Instrumented with SMART Layer sensors, this area surrounding the door also is being tested in two ground validators: an A350 barrel section and a fuselage shell section that has been impacted FIG. 2: In-service testing This network of SMART Layer sensors (left) is currently undergoing fight testing as a local SHM system for impact detection on an A350 CFRP door surround panel. A handheld diagnostic unit plugged into the SMART layer sockets (right) will indicate damage location and size or display a red/green signal, indicating damage/no damage in the structure. Source (left) | Airbus Source (right) | Acellent Technologies